Preparation of dicarboxylic anhydrides

ABSTRACT

A catalyst complex useful for the partial oxidation of alkanes to the corresponding anhydrides, e.g., converting normal C 4  hydrocarbons to maleic anhydride in vapor phase, comprising as components vanadium, phosphorus, oxygen, Nb, Cu, Mo, Ni, Co and Cr and one or more of Y, Sm, Tb or Eu. Preferred are those compositions containing in addition one or more of Ce, Nd, Ba, Hf, U, Ru, Re, Li or Mg.

This is a division, of application Ser. No. 767,499 filed Feb. 10, 1977now U.S. Pat. No. 4,105,586.

BACKGROUND OF THE INVENTION

The present invention relates to an improved process for the preparationof dicarboxylic anhydride from C₄ -C₁₀ hydrocarbons preferably using afeed containing major amounts of alkanes, by the reaction of oxygen withthe hydrocarbon in vapor phase over a particular novel catalyst, such asthe preparation of maleic anhydride from butane.

The production of dicarboxylic acid anhydride by catalytic oxidation ofhydrocarbons is well known. The current principal route for theproduction of maleic anhydride from C₄ hydrocarbons has been desirablein the past, but is now even more desirable in view of the particularworld shortage of benzene. It can be readily appreciated that directoxidation of C₄ hydrocarbons would be a hydrocarbon conservation, sincefor each mol of maleic anhydride prepared from benzene, one mol ofbenzene, molecular weight 78 is consumed, whereas for each mol of theC₄, only 54 to 58 mol weight of hydrocarbon is consumed. The benzeneprocess has consistently produced high conversions and selectivities.Although processes for the oxidation of aliphatic hydrocarbons arereported in the literature, there are certain defects and inadequaciesin these processes, such as short catalyst life and low yields ofproduct. Furthermore, although many of the prior art methods aregenerically directed to "aliphatic" hydrocarbons, they are in allpractical aspects directed to unsaturated aliphatic hydrocarbons.

A more desirable process for producing maleic anhydride would be adirect oxidation of n-butane. There are several advantages. Principalamong these is the greater availability of n-butane as compared ton-butenes or butadiene. Also, n-butenes may have higher economicpetrochemical utilization than the n-butanes, which are now, oftenwastefully burned as cheap fuel.

In an early series of patents, the present inventor developed a uniquegroup of vanadium-phosphorus, oxidation catalysts, i.e., U.S. Pat. Nos.3,156,705; 3,156,706; 3,255,211; 3,255,212; 3,255,213; 3,288,721;3,351,565; 3,366,648; 3,385,796 and 3,484,384. These processes andcatalysts proved highly efficient in the oxidation of n-butenes tomaleic anhydride. Since the issuance of these pioneer patents, numerouspatents have issued with various modification and improvements over thebasic discoveries set forth there, e.g., U.S. Pat. Nos. 3,856,824;3,862,146; 3,864,280; 3,867,411 and 3,888,886.

Most recently, the present inventor discovered thatvanadium-phosphorus-oxygen complex type catalyst modified with aparticular group of components is an excellent oxidation catalyst forthe conversion of C₄ to C₁₀ hydrocarbons to the correspondinganhydrides, particularly, n-C₄ hydrocarbons to maleic anhydride, whichis disclosed and claimed in U.S. Pat. No. 4,056,487 issued Nov. 1, 1977.In addition to n-butane, n-butene and butadiene may also be used asfeeds. The catalyst contains only a minor amount of the modifyingcomponent. The essential elements of the modifying component are Nb, Cu,Mo, Ni, Co and Cr. In addition to the essential elements, the modifyingcomponent may contain one or more elements from the group of Ce, Nd, Ba,Hf, U, Ru, Re, Li or Mg. The elements comprising the modifyingcomponents are metal or metalloid in characterization.

SUMMARY OF THE INVENTION

Very briefly, what the present inventor has discovered is an additionalgroup of modifying elements selected from the group consisting of Y, Sm,Tb and Eu. That is, the present invention is avanadium-phosphorus-oxygen complex type catalyst for the conversion ofC₄ to C₁₀ hydrocarbons to the corresponding anhydrides in which thecatalyst contains the essential modifying elements of Nb, Cu, Mo, Ni, Coand Cr, and one or more of the elements selected from the groupconsisting of Y, Sm, Tb and Eu. In addition to these newly discoveredmodifiers, the catalyst may also contain one or more of the elementsfrom the group consisting of Ce, Nd, Ba, Hf, U, Ru, Re, Li or Mg. Thepreferable components from my prior compositions, which are additionallypresent, are one or more of the elements selected from the groupconsisting of Ce, Nd and Ba. The improved catalyst containing thesemodifiers include those that have demonstrated superior performance.

One type of preferred catalyst contains in the modifier, Y and Sm,preferably with the addition of Nd, Ce and Ba.

The precise structure of the present complex catalyst has not beendetermined; however, the complex may be represented by formula

    VP.sub.a Me.sub.b O.sub.x

wherein Me is the modifying component described above, a is 0.90 to 1.3,b is 0.005 to 0.4. This representation is not an empirical formula andhas no significance other than representing the atom ratio of the activemetal components of the catalyst. The x, in fact, has no determinatevalue and can vary widely, depending on the combinations within thecomplex. That there is oxygen present is known and the O_(x) isrepresentative of this.

The following listing shows the ranges of each member of the complex,including the modifying component. The relative proportions are shown inatomic ratio relative to vanadium which is designated as 1. The amountsof components are selected within these ranges so that the total atomsof modifying component stays within the range given above, i.e., 0.005to 0.4 atom per atoms of vanadium.

    ______________________________________                                        Catalyst           Atomic                                                     Component          Ratio                                                      ______________________________________                                        V                  1                                                          P                  0.90-1.3                                                   Nb                 0.001-0.125                                                Cu                 0.022-0.201                                                Mo                 0.0025-0.040                                               Ni                 0.0022-0.045                                               Co                 0.0040-0.066                                               Ce                 0.0054-0.20                                                Nd                 0.0022-0.20                                                Cr                 0.0003-0.003                                               Ba                 0.0023-0.0585                                              Hf                 0.0023-0.0409                                              U                  0.0033-0.0993                                              Ru                 0.0002-0.02015                                             Re                 0.0002-0.0074                                              Li                 0.0072-0.179                                               Mg                 0.0088-0.222                                               Y                  0.0001-0.02                                                Sm                 0.0001-0.02                                                Tb                 0.0001-0.02                                                Eu                 0.0001-0.02                                                ______________________________________                                    

The relative amounts of the elements in the modifier as embraced by thisspecies are set forth above and when combined with the essentialcomponents give a total of 0.005 to 0.4 atom of modifier per atom ofvanadium, preferably, at least 0.033 of modifier per atom of vanadium.

The oxygen atomic ratio may vary widely, generally in the range of 5 to8, for the catalyst compositions of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst may be prepared in a number of ways. The catalyst may beprepared by dissolving compounds of vanadium, phosphorus, and othercompound components, i.e., Nb, Cu, Mo, Ni, Co, Ce, Nd, Cr, Ba, Hf, U,Ru, Re, Y, Sm, Tb, Eu, Li or Mg in a common solvent, such as hothydrochloric acid and thereafter depositing the solution onto a carrier.The catalyst may also be prepared by precipitating the variouscompounds, either with or without a carrier from a colloidal dispersionof the ingredients in an inert liquid. In some instances, the catalystmay be deposited as molten various compounds onto a carrier; however,care must be taken not to vaporize off any of the ingredients such asphosphorus. The catalyst may also be prepared by heating and mixinganhydrous forms of phosphorus acids with vanadium compounds andcompounds of the other components. The catalyst may be used as eitherfluid bed or fixed bed catalysts. In any of the methods of preparation,heat may be applied to accelerate the formation of the complex.

One method to obtain catalyst comprises forming the catalyst complex insolution and deposited as a solution onto niobium oxide (Nb₂ O₅).According to one solution method, the vanadium is present in solutionwith an average valence of less than plus 5 in the finally formedcomplex in solution. Preferably, the vanadium has an average valency ofless than plus 5 at the time the solution of catalyst complex isdeposited onto the carrier, if a carrier is used. The reduced vanadiumwith a valence of less than 5 may be obtained either by initially usinga vanadium compound wherein the vanadium has a valence of less than 5,such as vanadyl chloride, or by initially using a vanadium compound witha valence of plus 5, such as V₂ O₅, and thereafter reducing to the lowervalence with, for example, hydrochloric acid during the catalystpreparation to form the vanadium oxysalt, vanadyl chloride, in situ. Thevanadium compound may be dissolved in a reducing solvent, such ashydrochloric acid, which solvent functions not only to form a solventfor the reaction, but also to reduce the valence of the vanadiumcompound to a valence of less than 5. Preferably, the vanadium compoundis first dissolved in the solvent and thereafter the phosphorus andother metal (metalloid) compounds are added. The reaction to form thecomplex may be accelerated by the application of heat. The deep bluecolor of the solution shows the vanadium has an average valence of lessthan 5. The complex formed is then, without a precipitation step,deposited as a solution onto the Nb₂ O₅ and dried. In this procedure,the vanadium has an average valence of less than plus 5, such as aboutplus 4, at the time it is deposited onto the Nb₂ 0₅. Generally, theaverage valence of the vanadium will be between about plus 2.5 and 4.6at the time of deposition onto the carrier.

When the above described solution method is employed, reducing agentsfor the vanadium may be either organic or inorganic. Acids such ashydrochloric, hydroiodic, hydrobromic, acetic, oxalic, malic, citric,formic and mixtures thereof, such as a mixture of hydrochloric andoxalic may be used. Sulfur dioxide may be used. Less desirably, sulfuricand hydrofluoric acids may be employed. Other reducing agents which maybe employed, but which have not been given as desirable catalysts areorganic aldehydes such as formaldehyde and acetaldehyde; alcohols suchas pentaerythritol, diacetone alcohol and diethanol amine. Additionalreducing agents are such as hydroxyl amines, hydrazine and nitric oxide.Nitric acid and similar oxidizing acids which would oxidize the vanadiumfrom a valence of 4 to 5 during the preparation of the catalyst shouldbe avoided. Generally, the reducing agents form oxysalts of vanadium.For example, if V₂ O₅ is dissolved in hydrochloric or oxalic acid, thecorresponding vanadium oxysalts are produced. These vanadium oxysaltsshould have as the salt forming anion, an anion which is more volatilethan the phosphate anion.

Any vanadium, phosphorus and metal and metallid compounds may be used asstarting materials which, when the compounds are combined and heated todryness in air at a temperature of, for example, 300°-350° C. will leaveas a deposit a catalyst complex having relative proportions within thedescribed ranges. In the solution methods, preferred are vanadium,phosphorus and metal and metalloid (except Nb) compounds, which areessentially completely soluble in boiling aqueous hydrochloric acid at760 mm. of mercury, containing 37 percent by weight hydrochloric acid.Generally, phosphorus compounds are used which have as the cation an ionwhich is more volatile than the phosphate anion, for example, H₃ PO₄.Also, generally any vanadium or Me compound which has as an anion, ananion which is either the phosphate ion or an ion which is more volatilethan the phosphate anion, for example, vanadyl chloride or copperchloride, nickel chloride or the like may be used.

In the various methods of preparation, any vanadium, phosphorus, metaland metalloid compounds may be used as starting materials which, whenthe compounds are combined and heated to dryness in air at a temperatureof, for example, 300°-350° C., will leave as a deposit a catalystcomplex having relative proportions within the above described ranges.

In another method, a solution of the vanadium component is prepared byadding a portion of a reducing agent, such as oxalic acid andisopropanol solution to a solution of water and phosphoric acid, andheating this mixture to a temperature generally of around 50°-80° C. Avanadium compound such as V₂ O₅ is added incrementally to this heatedmixture with stirring. The blue solution which indicates vanadium ofaverage valency less than 5, is maintained by adding increments of theremaining oxalic acid-isopropanol solution. After concentration of thissolution, solutions of other components are added to vanadium solutionand this resultant solution concentrated to a paste-like consistency,and intimately mixed with Nb₂ O₅, heated at moderate temperature, i.e.,200°-400° C. for a few minutes to several hours and prepared in pelletsor chips.

As the source of phosphorus, various phosphorus compounds may be used,such as metaphosphoric acid, triphosphoric acid, pyrophosphoric acid,ortho-phosphoric acid, phosphorus pentoxide, phosphorus oxyiodide, ethylphosphate, methyl phosphate, amine phosphate, phosphorus pentachloride,phosphorus trichloride, phosphorus oxybromide and the like.

Suitable vanadium compounds useful as starting materials are compoundssuch as vanadium pentoxide, ammonium metavanadate, vanadium trioxide,vanadyl chloride, vanadyl dichloride, vanadyl trichloride, vanadiumsulfate, vanadium phosphate, vanadium tribromide, vanadyl formate,vanadyl oxalate, metavanadic acid, pyrovanadic acid, and the like.Mixtures of the various vanadium, phosphorus and metal and metalloidcompounds may be used as starting materials to form the describedcatalyst complex.

The metal or metalloid component is also suitably introduced byemploying the various compounds thereof such as the acetates,carbonates, chlorides, bromides, oxides, hydroxides, nitrates,chromates, chromites, tellurates, sulfides, phosphates and the like. Thecompounds are entirely conventional and those of ordinary skill in theart know these materials and can readily determine suitable compounds toprepare the catalyst, with little, if any, experimentation. A fewillustrative compounds are nickel chloride, chromium sulfate, chromiumtrioxide, chromium chloride, barium chloride and similar compounds.

A catalyst support, if used, provides not only the required surface forthe catalyst, but gives physical strength and stability to the catalystmaterial. The carrier or support normally has a low surface area, asusually measured from about 0.110 to about 5 square meters per gram. Adesirable form of carrier is one which has a dense non-absorbing centerand a rough enough surface to aid in retaining the catalyst adheredthereto during handling and under reaction conditions. The carrier mayvary in size but generally is from about 21/2 mesh to about 10 mesh inthe Tyler Standard screen size. Alundum particles as large as 1/4 inchare satisfactory. Carriers much smaller than 10 to 12 mesh normallycause an undesirable pressure drop in the reactor, unless the catalystsare being used in a fluid bed apparatus. Very useful carriers areAlundum and silicon carbide or Carborundum. Any of the Alundums or otherinert alumina carriers of low surface may be used. Likewise, a varietyof silicon carbides may be employed. Silica gel may be used.

The amount of the catalyst complex on the carrier is usually in therange of about 15 to about 95 weight percent of the total weight ofcomplex plus carrier and preferably in the range of 50 to 90 weightpercent and more preferably at least 60 weight percent on the carrier.The amount of the catalyst complex deposited on the carrier should beenough to substantially coat the surface of the carrier and thisnormally is obtained with the ranges set forth above. With moreabsorbent carriers, larger amounts of material will be required toobtain essentially complete coverage of the carrier. In a fixed bedprocess, the final particle size of the catalyst particles which arecoated on a carrier will also preferably be about 21/2 to about 10 meshsize. The carriers may be of a variety of shapes, the preferred shape ofthe carriers is in the shape of cylinder or spheres. Although moreeconomical use of the catalyst on a carrier in fixed beds is obtained,as has been mentioned, the catalyst may be employed in fluid bedsystems. Of course, the particle size of the catalyst used in fluidizedbeds is quite small, usually varying from about 10 to about 150 microns,and in such systems the catalyst normally will not be provided with acarrier, but will be formed into the desired particle size after dryingfrom solution.

Inert diluents may be present in the catalyst, but the combined weightof the active ingredients, e.g., vanadium, oxygen, phosphorus, metal andmetalloid should preferably consist essentially of at least about 50weight percent of the composition which is coated on the carrier, ifany, and preferably these components are at least about 75 weightpercent of the composition coated on the carrier, and more preferably,at least about 95 weight percent.

The niobium component of the present composition is preferably niobiumoxide, Nb₂ O₅, which is intimately mixed with the other components ofthe catalysts, which are in solution.

In one procedure for preparing the present catalyst compositions, thevanadium component is prepared by adding a portion of a reducing agent,such as an oxalic acid with or without isopropanol, to a solution ofwater and phosphoric acid and heating this mixture to a temperaturegenerally around 50°-60° C. A vanadium compound, such as V₂ O₅ is slowlyadded while raising the temperature of the solution to 60°-90° C. A bluesolution indicates vanadium of average valency of less than 5 at whichtime the molybdenum component as MoO₃ is added to the solution anddissolved therein.

The V-P-Mo mixture is added to a powdered Nb₂ O₅ and mixed together at75°-95° C. in a suitable mixer to obtain intimate contact. The remainderof the catalyst components are added to this mixture as solutions,preferably of the chloride salts, e.g., obtained by dissolving oxidesand/or carbonates in HCl.

Thus, this method of catalyst preparation involves two particularaspects. First, the vanadium is reduced with a reducing agent in asolution containing phosphoric acid and second, a majority (over 50% bycomponent) of the remaining catalyst components are employed as thechloride salts. In particular, Ni, Co, Cu, Cr, Nd, Ce, Ba, Hf, Y, Sm, Tband Eu are employed as chloride salts. All of the metal and metalloidelements employed in preparing the catalyst, with the exception ofvanadium, phosphorus and niobium may be used as the chloride salt.

The resulting mixture is dried at 85°-135° C. and broken into pieces of4 to 20 mesh and dried further at 120°-130° C. then heated at 300° C.for an additional period of 0.5 to two or three hours. The catalyst maybe used as such, but is preferably reduced to a powder and pelleted. Asnoted above, binders, such as stearic acid, carriers and inert fillersmay be added before pelleting.

The oxidation of the n-C₄ hydrocarbon to maleic anhydride may beaccomplished by contacting, e.g., n-butane, in low concentrations inoxygen with the described catalyst. Air is entirely satisfactory as asource of oxygen, but synthetic mixtures of oxygen and diluent gases,such as nitrogen, also may be employed. Air enriched with oxygen may beemployed.

The gaseous feed stream to the oxidation reactors normally will containair and about 0.5 to about 2.5 mol percent hydrocarbons, such asn-butane. About 1.0 to about 1.7 mol percent of the n-C₄ hydrocarbonsare satisfactory for optimum yield of product for the process of thisinvention. Although higher concentrations may be employed, explosivehazards may be encountered. Lower concentrations of C₄, less than aboutone percent, of course, will reduce the total yields obtained atequivalent flow rates and thus are not normally economically employed.The flow rate of the gaseous stream through the reactor may be variedwithin rather wide limits, but a preferred range of operations is at therate of about 50 to 300 grams of C₄ per liter of catalyst per hour andmore preferably about 100 to about 250 grams of C₄ per liter of catalystper hour. Residence times of the gas stream will normally be less thanabout 4 seconds, more preferably less than about one second, and down toa rate where less efficient operations are obtained. The flow rates andresidence times are calculated at standard conditions of 760 mm. ofmercury and at 25° C. An improved output of maleic anhydride can beobtained with various catalysts of the prior art with those of thepresent invention if the feed consists essentially of C₄ normal alkane,i.e., about comprising 88 to 99 or more weight percent normal C₄ alkaneand from about 1 to 12 weight percent n-butene, benzene, or a mixturethereof. A preferred feed for the catalyst of the present invention forconversion to maleic anhydride is a n-C₄ hydrocarbon comprising apredominant amount of n-butane and more preferably, at least 90 molpercent n-butane.

A variety of reactors will be found to be useful and multiple tube heatexchanger type reactors are quite satisfactory. The tubes of suchreactors may vary in diameter from about 1/4 inch to about 3 inches, andthe length may be varied from about 3 to about 10 or more feet, e.g., 12feet. The oxidation reaction is an exothermic reaction and, therefore,relatively close control of the reaction temperature should bemaintained. It is desirable to have the surface of the reactors at arelatively constant temperature and some medium to conduct heat from thereactors is necessary to aid temperature control. Such media may beWoods metal, molten sulfur, mercury, molten lead, and the like, but ithas been found that eutectic salt baths are completely satisfactory. Onesuch salt bath is a sodium nitrate-sodium nitrite-potassium nitrateeutectic constant temperature mixture. An additional method oftemperature control in the laboratory is to use a metal block reactorwhereby the metal surrounding the tube acts as a temperature regulatingbody. As will be recognized by the man skilled in the art, the heatexchange medium may be kept at the proper temperature by heat exchangersand the like. The reactor or reaction tubes may be iron, stainlesssteel, carbon steel, nickel, glass tubes, such as Vycor, and the like.Both carbon steel and nickel tubes have excellent long life under theconditions of the reactions described herein. Normally, the reactorscontain a preheat zone of an inert material such as 1/4 inch Alundumpellets, inert ceramic balls, nickel balls or chips and the like,present at about one-half to one-tenth the volume of the active catalystpresent.

The temperature of reaction may be varied within some limits, butnormally, the reaction should be conducted at temperatures within arather critical range. The oxidation reaction is exothermic and oncereaction is underway, the main purpose of the salt bath or other mediais to conduct heat away from the walls of the reactor and control thereaction. Better operations are normally obtained when the peak reactiontemperature employed is no greater than about 100° C. above the saltbath temperature. The temperature in the reactor, of course, will alsodepend to some extent upon the size of the reactor and the C₄concentration. Under usual operating conditions, in compliance with thepreferred procedure of this invention, the temperature in the center ofthe reactor, measured by thermocouple, is about 375° C. to 550° C. Therange of temperature preferably employed in the reactor, measured asabove, should be from about 390° C. to about 460° C., and the bestresults are ordinarily obtained at temperatures from about 410° C. toabout 450° C.

Described another way, in terms of salt bath reactors with carbon steelreactor tubes about 1.0 inch in diameter, the salt bath temperature willusually be controlled between about 350° C. to about 450° C. Undernormal conditions, the temperature in the reactor ordinarily should notbe allowed to go above about 450° C. for extended lengths of timebecause of decreased yields and possible deactivation of the novelcatalyst of this invention.

The reaction may be conducted at atmospheric, super-atmospheric orbelow-atmospheric pressure. The exit pressure will be at least slightlyhigher than the ambient pressure to insure a positive flow from thereaction. The pressure of the inert gases may be sufficiently high toovercome the pressure drop through the reactor.

In one utilization of the present catalyst compositions, the oxidationis carried out at 15 to 100 psig, preferably about 20 to 50 psig, andmore preferably about 25 to 40 psig.

Operating under pressure as described above, the temperature in thecenter of the reactor, measured by thermocouple is about 375° C. toabout 550° C. with the preferred temperature range for operatingaccording to the present invention being 430° C. to 480° C. and the bestresults are ordinarily obtained at temperatures from about 430° C. toabout 455° C. Described another way, in terms of salt bath reactors withcarbon steel reactor tubes about 1.0 inch in diameter, the salt bathtemperature will usually be controlled between about 325° C. to about440° C. Under these conditions, the temperature in the reactorordinarily should not be allowed to go above about 450° C. for extendedlengths of time because of decreased yields and possible deactivation ofthe novel catalyst of this invention.

The maleic anhydride may be recovered by a number of ways well known tothose skilled in the art. For example, the recovery may be by adsorptionin suitable media, with subsequent separation and purification of themaleic anhydride.

In the following examples, percents are by weight unless otherwisespecified.

The reactor used to evaluate the catalyst compositions employed 300milliliters of catalyst packed in a 3-foot carbon steel tube, 3/4 inchinside diameter (or equivalent), with inert 1/4 inch Alundum pellets ontop of the catalyst material to a height 1/3 of the height of thecatalyst.

The reactors were encased in a 7% sodium nitrate-40% sodium nitrite-53%potassium nitrate eutectic mixture constant temperature salt bath. Thereactor was slowly warmed to 400° C. (250°-270° C. air passing overcatalyst) while passing a gas stream containing 0.5 to 0.7 mol percentn-butane and air over the catalyst beginning at about 280° C. Thereactor outlet was maintained at 1 psig. After the reactor had reached390° C., the catalyst was aged by passing the n-butane-air mixturetherethrough for 24 hours. The n-butane-air and temperature wasincreased to obtain a maximum throughput. The n-butane in the feed isincreased to 1.0-1.5 mol percent to obtain 70-80% conversion. The saltbath is operated at a maximum of 420° C. The maximum throughput isachieved in relation to the maximum salt bath temperature and a maximumhot spot of about 450° C. The hot spot is determined by a probe throughthe center of the catalyst bed. The temperature of the salt bath can beadjusted to achieve the desired relationship between the conversion andflow rates of the n-C₄ -air mixture. The flow rate is adjusted to about75% conversion and the temperature relations given above. Generally,flow rates of about 70 to 120 grams of hydrocarbon feed per liter hourare used. The exit gases were cooled to about 55°-60° C. at about 1/2psig. Under these conditions, about 30-50% of the maleic anhydridecondenses out of the gas stream. A water scrubber recovery andsubsequent dehydration and fractionation were used to recover and purifythe remaining maleic anhydride in the gas stream after condensation. Thecombined maleic anhydride recovered is purified and recovered at atemperature of about 140°-165° C. overhead and 165° C. bottomstemperatures in a fractionator. The purified product had a purity of99.9+ percent maleic anhydride.

EXAMPLES 1-5

    ______________________________________                                         EXAMPLE 1                EXAMPLE 2                                           ______________________________________                                        Ingredients:             Ingredients:                                         V.sub.2 O.sub.5                                                                        263.37    g     V.sub.2 O.sub.5                                                                         270.531 g                                  MoO.sub.3                                                                              4.18      g     MoO.sub.3 4.268   g                                  CuCl.sub.2 . 2H.sub.2 O                                                                44.386    g     CuCl.sub.2 . 2H.sub.2 O                                                                 45.279  g                                  NiO      3.304     g     NiO       3.373   g                                  CoCl.sub.2 . 6H.sub.2 O                                                                11.992    g     CoCl.sub.2 . 6H.sub.2 O                                                                 15.306  g                                  CrO.sub.3                                                                              0.418     g     CrO.sub.3 0.5355  g                                  BaCl.sub.2 . 2H.sub.2 O                                                                8.324     g     CeO.sub.2 2.6675  g                                  CeO.sub. 2                                                                             5.5       g     Nd.sub.2 O.sub.3                                                                        2.6675  g                                  Nd.sub.2 O.sub.3                                                                       5.5       g     HfO.sub.2 4.268   g                                  HfO.sub.2                                                                              4.18      g     Sm.sub.2 O.sub.3                                                                        22.0    g                                  Y.sub.2 O.sub.3                                                                        16.6      g     Nb.sub.2 O.sub.5                                                                        16.5    g                                  Nb.sub.2 O.sub.5                                                                       5.5       g                                                          ______________________________________                                        EXAMPLE 3                EXAMPLE 4                                            ______________________________________                                        Ingredients:             Ingredients:                                         V.sub.2 O.sub.5                                                                        263.382   g     V.sub.2 O.sub.5                                                                         267.269 g                                  MoO.sub.3                                                                              5.335     g     MoO.sub.3 4.268   g                                  CuCl.sub.2 . 2H.sub.2 O                                                                67.991    g     CuCl.sub.2 . 2H.sub.2 O                                                                 56.627  g                                  NiO      3.855     g     NiO       3.373   g                                  CoCl.sub.2 . 6H.sub.2 O                                                                15.306    g     CoCl.sub.2 . 6H.sub.2 O                                                                 13.777  g                                  CrO.sub.3                                                                              0.5335    g     CrO.sub.3 0.5335  g                                  BaCl.sub.2 . 2H.sub.2 O                                                                8.499     g     BaCl.sub.2 . 2H.sub.2 O                                                                 8.499   g                                  CeO.sub.2                                                                              5.5       g     CeO.sub.2 5.5     g                                  Nd.sub.2 O.sub.3                                                                       5.5       g     Nd.sub.2 O.sub.3                                                                        5.5     g                                  HfO.sub.2                                                                              4.268     g     HfO.sub.2 4.268   g                                  Tb.sub.4 O.sub.7                                                                       11.0      g     Eu.sub.2 O.sub.3                                                                        4.805   g                                  Nb.sub.2 O.sub.5                                                                       16.5      g     Nb.sub.2 O.sub.5                                                                        16.5    g                                  ______________________________________                                        EXAMPLE 5                                                                     ______________________________________                                        Ingredients:                                                                  V.sub.2 O.sub.5                                                                        1222.459  g                                                          MoO.sub.3                                                                              24.25     g                                                          CuCl.sub.2 . 2H.sub.2 O                                                                206.002   g                                                          NiO      17.524    g                                                          CoCl.sub.2 . 6H.sub.2 O                                                                71.726    g                                                          CrO.sub.3                                                                              2.425     g                                                          BaCl.sub.2 . 2H.sub.2 O                                                                38.632    g                                                          CeO.sub.2                                                                              50.0      g                                                          Nd.sub.2 O.sub.3                                                                       25.0      g                                                          Y.sub.2 O.sub.3                                                                        6.566     g                                                          Sm.sub.2 O.sub.3                                                                       3.740     g                                                          Nb.sub.2 O.sub.5                                                                       75.0      g                                                          ______________________________________                                        Reaction Mixture:                                                             EXAMPLE      1       2       3     4     5                                    ______________________________________                                        Distilled water ml.                                                                        2750    2750    2500  2750  10,000                               Oxalic acid g.                                                                             210     215     170   210   840                                  Isopropyl alcohol ml.                                                                      250     200     200   200   680                                  85% H.sub.3 PO.sub.4 ml.                                                                     227.7   231.0   227.7                                                                               229.1                                                                             1056.8                               HCl ml.      --      --      100   --    400                                  ______________________________________                                    

PROCEDURE, EXAMPLES 1-4 (Note - Example 5 is conducted on scaleapproximately four times that of Examples 1-4, and the procedure shouldbe adjusted accordingly.)

Heat the mixture to 50°-60° C. and add the V₂ O₅ slowly while raisingthe temperature to 65° C. to 85° C. After all of the V₂ O₅ is added,reflux slowly until the solution is homogeneous and blue. Reduce thevolume to 1500 ml. by taking off water and alcohol on reflux. Add theMoO₃ to the vanadyl phosphate solution and continue to reflux and reducethe volume to about 1000 ml. The Nb₂ O₅ is added to a tumbler, about 20liter size, and prewarmed to 40°-60° C. The concentrated V-P-Mo mixtureis then added to the tumbler. The heat source is increased to raise thetemperatures to 75°-90° C. and held there. The NiO is dissolved in 400ml. of HCl along with the CoCl₂.6H₂ O. The oxides are digested to thesoluble chlorides while reducing the HCl volume to 200 ml., 100 ml. ofH₂ O is added to the clear, dark solution. The Ni-Co mixture is thenadded to the V-P-Mo-Nb₂ O₅ mixture in the tumbler. The CuCl₂.2H₂ O isdissolved in 400 ml. of H₂ O and is added next; followed by CrO₃ in 50ml. of H₂ O. When the mixture becomes green and slightly viscous, Nd₂O₃, dissolved in H₂ O and HCl and CeO₂, dissolved in concentrated HCl,are added along with BaCl₂ (if any) in H₂ O, and shortly after this, theHfO₂, Y₂ O₃, Sm₂ O₃, Tb₄ O₇ and/or Eu₂ O₃ (as appropriate) are added.After heating and loss of water vapor, the mixture becomes more viscousand difficult to stir. It is then transferred to pyrex dishes. The greenmixture is dried from 85° C. to 100° to 135° C. over a 36-hour period.The solid mass is broken up to a 4 mesh, or less, and dried from 120° to300° C. over 4 hours; held at 300° C. for one hour. The chipped catalystis ball-milled in a dry atmosphere for 6 hours to obtain 60 mesh fines.To this is mixed 0.5% Curtin type graphite and 1% Baker stearic acid.1/8"×1/8" pellets are produced. The pellets are heated slowly to 300° C.so that they can be added directly to the hot salt reactor held at 250°C.

The conditions of the reactors and results of maleic anhydridepreparation from n-butane are set out below in Table 1.

                                      TABLE I                                     __________________________________________________________________________                              Butane                                               Ex.                                                                               ml.dia. Catalyst                                                                       SizeReactor                                                                         Salt   %MoleConc.perature                                                                g/l cat hrThruput                                                                  Conv. Sel YieldMole % Maleic                                                 Anhydride   g.MA/l.cat/hrOutput                                                                   ##STR1##               __________________________________________________________________________    1   300 1/8"×1/8"                                                                    3/4"×3'                                                                       396 408                                                                              1.10                                                                              74   685940     50      0.68                                       403429 1.43                                                                              140  715640     93      0.66                    2   300 1/8"×1/8"                                                                    3/4"×3'                                                                       398409 1.05                                                                              66   716244     49      0.74                                       407449 1.29                                                                              150  706243     109     0.72                    3   300 1/8"×1/8"                                                                    3/4"×3'                                                                       399415 1.01                                                                              66   705840     44      0.66                                       402440 1.33                                                                              132  715539     87      0.66                    4    300 1/8"×1/8"                                                                   3/4"×3'                                                                       400422 1.02                                                                              50   726245     38      0.76                                       403429 1.25                                                                              140  636239     92      0.66                    5  1850 3/16"×3/16"                                                                  1-1/4"×12'                                                                    389421 1.40                                                                              87   696746     68      0.78                                       388422 1.45                                                                              91   696746     71      0.78                                       392430 1.63                                                                              96   736648     79      0.82                    __________________________________________________________________________

These new catalysts are in every way at least equal to those disclosedin my U.S. Pat. No. 4,056,487, and are superior to many of those priorcatalysts. Note, in particular, the present catalyst of Example 5, whichexhibits excellent conversion for this reaction and superior selectivityfor MA. Although the conditions of Example 5 were not extended to thesame degree as the other examples, the ratio of MA output to butaneinput is highest for Example 5.

Butane was extensively employed in the present examples because of itsavailability and easy handling. The other C₄ -C₁₀ hydrocarbons,particularly, normal paraffins and olefins, also are suitable for use inconjunction with the present catalyst to produce anhydrides; forexample, n-pentane, n-hexane, n-heptane, n-octane, n-nonane and n-decaneand the corresponding olefins.

The invention claimed is:
 1. In a process for the partial oxidation ofC₄ to C₁₀ hydrocarbons to prepare the corresponding dicarboxylicanhydrides comprising contacting a feed containing to C₄ to C₁₀ alkanehydrocarbons in vapor phase at elevated temperatures, with oxygen and acatalyst composition wherein the improvement comprises a catalystcomposition consisting of vanadium, phosphorus and oxygen and amodifying component consisting of(a) the elements Nb, Cu, Mo, Ni, Co andCr, and (b) one or more elements selected from the group consisting ofY, Sm, Tb. and Eu. Ii(a) the elements Nb, Cu, Mo, Ni, Co and Cr, (b) oneor more of the elements selected from the group consisting of Ce, Nd,Ba, Hf, U, Ru, Re, Li or Mg, and (c) one or more of the elementsselected from the group consisting of Y, Sm, Tb and Eu,wherein theatomic ratio of vanadium:phosphorus:Nb:Cu:Mo:Ni:Co:Ce:Nd:Cr:Ba:Hf:U:Ru:Re:Li:Mg:Y:Sm:Tb:Eu is 1:0.90 to 1.3:0.001 to0.125:0.022 to 0.201:0.0025 to 0.040:0.0022 to 0.045:0.004 to0.066:0.0054 to 0.2:0.0022 to 0.20:0.0003 to 0.003:0.0023 to0.0585:0.0023 to 0.0409:0.0033 to 0.0993:0.0002 to 0.02015:0.0002 to0.0074:0.0072 to 0.179:0.0088 to 0.222:0.0001 to 0.02:0.0001 to0.02:0.0001 to 0.02:0.0001 to 0.02, respectively, the total atomic ratioof Nb, Cu, Mo, Ni, Co, Ce, Nd, Cr, Ba, Hf, U, Ru, Re, Li, Mg, Y, Sm, Tband Eu being in the range of 0.033 to 0.4.
 2. The process according toclaim 1 wherein said hydrocarbons is a normal hydrocarbon.
 3. Theprocess according to claim 2 wherein said normal alkane is n-butane. 4.The process according to claim 1 wherein said hydrocarbon comprisingabout 88 to 99 mol percent normal C₄ alkanes and from about 1 to 12 molpercent n-butene, benzene or a mixture thereof.
 5. The process accordingto claim 1 wherein said modifying component consists of (a) the elementsNb, Cu, Mo, Ni, Co and Cr, and (b) one or more of the elements selectedfrom the group consisting of Y, Sm, Tb and Eu.
 6. The process accordingto claim 5 wherein Y is a modifying component.
 7. The process accordingto claim 5 wherein Sm is a modifying component.
 8. The process accordingto claim 5 wherein Tb is a modifying component.
 9. The process accordingto claim 5 wherein Eu is a modifying component.